1. Field of the Invention
The present invention relates to a rotating anode X-ray tube which is capable of coping with the coolant leakage from a rotary seal, the coolant being for cooling the inside of the rotating anode, and also relates to an X-ray generator having such a rotating anode X-ray tube.
2. Description of the Related Art
A rotating anode of a rotating anode X-ray tube is cooled at its inside by cooling water. Since the rotating anode is rotated during cooling by the cooling water, its coolant passage must be sealed by a rotary liquid-tight sealing device such as a mechanical seal or an oil seal. The sealing function of the sealing region is maintained by, in general, an elastic force. When the liquid-tight property has been deteriorated because of roughness or wear of the seal surface, water leakage occurs little by little. When the leakage water adheres to parts such as a bearing, an electric brush or a vacuum sealing device, the lifetime of the parts would be shortened disadvantageously. Accordingly, it is desirable to improve the structure so that the leakage water does not adhere to the parts even when the water leakage occurs, or to detect soon the water leakage for prompting an exchange of the rotary fluid-tight sealing device. The prior art which is material to the present invention is as described below. Japanese patent publication No. 7-220667 A (1995), the first publication, discloses a basic structure of the rotating anode X-ray tube and a coolant sealing device. Japanese patent publication No. 2-197098 A (1990), the second publication, discloses a rotating anode X-ray tube having a water leakage sensor.
In the second publication, a rotating anode X-ray tube includes a vacuum chamber which houses therein a tray arranged below the anode or target. The tray can receive leakage water dropped away the anode. When stored water in the tray reaches a predetermined height, the water touches the sensor to generate a water leakage signal. When detecting the water leakage signal, generation of the electron beam is stopped and a buzzer sounds to call user's attention to water leakage.
The above-described water leakage sensor has a following problem. The water leakage sensor focuses attention on the water leakage dropped away the anode surface into the internal space of the vacuum chamber. Such water leakage is supposed to be water leakage from a coolant passage cropping out due to target erosion caused by electron beam collision, or water leakage from a weld joint of the target.
The above-described water leakage sensor, however, can not cope with water leakage little by little caused by deterioration of a coolant sealing device. When the water leakage from the coolant sealing device occurs, water does not drop away the anode into the vacuum chamber but enters into the internal space of the casing which rotatably supports the rotating anode. When such water leakage occurs, the lifetime of parts, such as a bearing, an electric brush or a vacuum sealing device, housed in the casing is shortened disadvantageously as has been described above. The water leakage sensor disclosed in the second publication can not cope with such water leakage. Furthermore, the leakage water little by little from the coolant sealing device is not in the form of liquid but is in the form of fine-atomized droplets or vapor, which may disperses into the internal space of the casing. The type of water leakage sensor which stores water in a tray can not always detect such water leakage and can not early detect a trace of water leakage. At the stage of a trace of water leakage, it would be effective to let out water in the form of vapor to the atmosphere to prolong the lifetime of parts, but such a thing is impossible in the prior art disclosed in the second publication.